The use of classification is to facilitate the work both of the author or teacher, and of the student. To the former it is highly advantageous by affording him the opportunity of presenting, in one view, and in a comparatively few words, all the common properties and uses of any number of bodies; so that, in the subsequent description of these bodies severally, he may omit whatever is not peculiar to each, and thus spare himself a vast amount of repetition. To the latter it is almost essential; as, by fixing in his mind the properties of classes, and thus serving to recall these properties in relation to any individual, upon the recollection simply that it belongs to the class, it aids his memory beyond all other contrivance, and enables him to gather and retain an amount of knowledge, which would be quite unattainable were he to study each object in an isolated state. The only kind of works in which classification is unnecessary are those intended, not for continuous study, but for occasional reference, when information is desired upon some particular name or object, such as dictionaries, encyclopedias, and, to a certain extent. dispensatories, in all of which an alphabetical arrangement is most convenient.

The advantages and even necessity of classification being admitted, the next point for consideration is the plan to be adopted. Now it may be asserted, without fear of contradiction, that no plan is faultless. Every mode of classification which has been proposed in relation to remedies has its disadvantages; and it is, therefore, no valid objection to any particular one which may be suggested that it is not prefect That one, it appears to me, is the best, which best promotes the great object of all classification; the facilitating, namely, of the acquisition of knowledge. As different kinds of knowledge are required of the same bodies by different sets of students, it follows that the classification should be different also; for, to be productive of the most good, it must be based upon the relation of the bodies to one another in those proper-ties which are the special object of study. Thus, in reference to medicines, the intention may be to study them as objects either of natural history, pharmaceutical management, or therapeutic use and they should be arranged accordingly. Their classification, therefore, should be based, for the general student, upon their geological, botanical, or mineralogical relations; for the pharmaceutist, either upon their chemical properties, or their resemblance in modes of preparation; for the therapeutist, undoubtedly upon their effects on the system, through which they become applicable to the cure of disease. It is in the last-mentioned capacity that they are important to the physician; and in this especially he should be taught, from the earliest period of his studies. to regard them. As, therefore, the present work is devoted more especially to the therapeutic consideration of medicines, I have, without hesitation, adopted a system of classification, founded upon their relations to one another in their modes of affecting the human system.

The question now occurs, admitting the effects of medicines to afford the true basis of classification, whether it is their physiological or therapeutical effects to which we should have recourse. At the first glance it might be supposed that the latter should be preferred. But a little consideration will decide against them. Formerly, when the notion prevailed that there were specific remedies for particular diseases, or classes of disease, an arrangement of medicines based on this principle was to a certain extent naturally adopted. Hence the terms antiphlo-gistics, febrifuges, antispasmodics, antiscorbutics, antisyphilitics, anti-lithics, etc. But the fact is, that there is no specific, strictly speaking; that is, there is no remedy which is especially adapted to one disease, and one only, and no curable disease which will yield only to one remedy; and, in relation to classes of disease, such as inflammations, fevers, and spasmodic affections, there is no one which does not require, in different stages, and under different circumstances, the same medicines found useful in the others; so that classes founded on this basis would be constantly clashing, each containing the individuals embraced by the others; and thus all the advantages of classification would be lost. For example, in the treatment of the three sets of diseases above mentioned, in one or another of their stages or varieties, we employ bleeding, cathartics, emetics, narcotics, tonics, stimulants, revulsives, etc. The physiological effects must, therefore, be resorted to; and, happily, it will be found that, to one well acquainted with pathology, these very effects, and consequently the medicines producing them, are suggested by the therapeutic indications. It will be perceived that, in the following plan, all the old classes founded on the therapeutic basis, as antispasmodics and antilithics, have been abandoned, and, except in the instances of the last five or six, which do not act on the system itself, but on extraneous matters accidentally contained within it, and operating as causes of disease, all the classes have a purely physiological relation. I wish it to be specially noticed that, in distributing remedies in the following classes, I am fully aware that the members of one class often possess properties which characterize another; and that, in deciding in which to place them, I have been in many instances influenced by their practical use, giving them a position in accordance with those properties which, if not always most striking, are those which constitute their chief value as medicines, or at least for which they are most employed.